The present invention relates to inhalers and in particular inhalers for the delivery of a medicament to the lung, more particularly a medicament in powder form.
In recent times, there has been a growing interest in the systemic delivery of pharmaceutically-active medicaments via the lung. Such a method of delivery is generally more attractive to the patient than methods such as injection, because it does not involve a needle and can be carried out discreetly in public.
For a medicament in a particulate form the provision of an inhalable aerosol requires an inhaler that can produce a repeatable dose of fine particles. In order for the particles of medicament to reach the lung and thus be absorbed into the bloodstream, the particles must have an effective diameter in the range of approximately 1 to 3 microns. The portion of the emitted aerosol within this range of particle size is known as the “fine particle fraction”. If the particles are larger than 5 microns they may not be transported by the inhaled airflow deep into the lung, because they are likely to be trapped in the respiratory passages before reaching the deep lung. For example, particles of the order of 10 microns are unlikely to progress further than the trachea and particles of the order of 50 microns tend to deposit on the back of the throat when inhaled. Furthermore, if the particles are less than 1 micron in effective diameter, the particles may not be absorbed in the lung, because they are small enough to be expelled from the lung with the exhaled airflow.
Thus, it will be seen that it is important that a powdered medicament is delivered with an accurately controlled range of particle size in order that it is absorbed effectively in the lung.
In traditional metered dose inhalers (MDIs) it is common for the emitted dose (the amount of medicament that enters the patient's airway) to be around 80 to 90% of the dose ejected from the inhaler. The fine particle fraction may be only around 50% of the emitted dose. However, the variation in the fine particle fraction of known inhalers can be ±20 to 30%. Such variation may be acceptable in the case of asthma drugs and the like, but when the medicament is a more potent drug such as insulin, growth hormone or morphine, this amount of variability in the dosing is unacceptable. The relatively low fine particle fraction also represents a significant wastage of what may be an expensive drug. Furthermore, there may be side effects if the proportion of the emitted dose which is not respired is swallowed.
Thus, it is important for the systemic delivery of medicaments by inhalation that a repeatable dose of fine particles can be produced.
WO 90/15635 describes a device for the pulverisation of particles or agglomerates of a powdered inhalation medicament comprising a rotationally symmetrical vortex chamber with spaced inlet and outlet ports. The inlet port directs air inflow into the vortex chamber substantially parallel to the tangent of the chamber. In one arrangement the chamber has a central outlet port.
WO 01/00262 discloses an inhaler comprising a pump, a drug dosing device and a cyclone, which delivers an aerosol of powdered medicament from the drug dosing device into a chamber when the pump is activated. The aerosol is inhaled by the user through a mouthpiece. The cyclone comprises a cylindrical chamber with an axial outlet and a tangential inlet.
Particles of medicament can be separated by generating shear forces between the particles, for example by providing a substantial velocity gradient across the particles. This may be done, for example, by forcing the powder through a narrow nozzle at high speed or introducing the powder into a turbulent air stream. Alternatively, a cyclone of the type described in WO 01/00262 can be used.